Levothyroxine formulations

ABSTRACT

A levothyroxine composition includes levothyroxine sodium and mannitol. The composition is a solid. The composition may include from 100 to 500 micrograms levothyroxine sodium and from 1 to 5 milligrams mannitol. The composition may include from 100 to 200 micrograms levothyroxine sodium, and the mass ratio of mannitol to levothyroxine sodium in the composition may be at most 40:1. The composition may include about 500 micrograms levothyroxine sodium, and the mass ratio of mannitol to levothyroxine sodium in the composition may be at most 10:1.

REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/529,084 entitled “Levothyroxine Formulations” filed Aug. 30, 2011,which is incorporated by reference in its entirety.

BACKGROUND

A healthy thyroid produces hormones that regulate multiple metabolicprocesses and that play important roles in growth and development, inmaturation of the central nervous system and bone including augmentationof cellular respiration and thermogenesis, and in metabolism ofproteins, carbohydrates and lipids. The thyroid accomplishes itsregulation functions by producing the hormones L-triiodothyronine(liothyronine; T3) and L-thyroxine (levothyroxine; T4).

Thyroid hormones are believed to exert their physiologic actions throughcontrol of DNA transcription and protein synthesis. It is presentlybelieved that the T3 and T4 hormones diffuse into the cell nucleus andbind to thyroid receptor proteins attached to DNA. This hormone nuclearreceptor complex then activates gene transcription and synthesis ofmessenger RNA and cytoplasmic proteins. The physiological actions ofthyroid hormones are believed to be produced predominantly by T3,approximately 80% of which is derived from T4 by deiodination inperipheral tissues.

Both T3 and T4 are stored in the thyroid as thyroglobulin adducts withserum proteins. Once secreted by the thyroid, T3 and T4 primarily existin the circulatory system as their thyroglobulin adducts, and are inequilibrium with small amounts (<1%) of the unbound hormones, which arethe metabolically active species. T4 has higher serum levels, slowermetabolic clearance, and a longer half-life than T3, which may be due tothe higher affinity of serum proteins for T4 compared to T3.

A patient who has had their thyroid gland removed, or whose thyroidgland functions at an undesirably low level (hypothyroidism), may betreated by administration of a daily maintenance dose of 50-100micrograms (μg) of levothyroxine sodium. A patient in need of additionalintervention may be treated by administration of an initial dose of200-500 μg or 300-500 μg of levothyroxine sodium and/or with a 2^(nd)day dose of 100-300 μg of levothyroxine sodium. Formal names forlevothyroxine sodium include4-(4-hydroxy-3,5-diiodophenoxy)-3,5-diiodo-L-phenylalanine sodium, andL-tyrosine-O-(4-hydroxy-3,5-diiodophenyl)-3,5-diiodo-monosodium salt.The chemical structure of levothyroxine sodium is shown in FIG. 1.

Administration of levothyroxine sodium provides T4 to a patient. Onceabsorbed by the organism, the administered T4 behaves identically to T4that otherwise would be secreted by the thyroid gland of the patient,and binds to the same serum proteins, providing a supply of circulatingT4-thyroglobulin in the patient. The administered T4 may be deiodinatedin vivo to T3. As a result, a patient receiving appropriate doses oflevothyroxine sodium will exhibit normal blood levels of T3, even whenthe patient's thyroid gland has been removed or is not functioning.

Levothyroxine sodium for injection is a sterile lyophilized product forparenteral administration of levothyroxine sodium for thyroidreplacement therapy. Levothyroxine sodium for injection is particularlyuseful when thyroid replacement is needed on an urgent basis, for shortterm thyroid replacement, and/or when oral administration is notpossible, such as for a patient in a state of myxedema coma.

Conventional formulations of levothyroxine sodium for injection arepreservative-free lyophilized powders containing synthetic crystallinelevothyroxine sodium and the excipients mannitol, tribasic sodiumphosphate, and sodium hydroxide. These conventional formulationstypically contain 10 milligrams (mg) of mannitol, 700 μg of tribasicsodium phosphate, and either 200 μg or 500 μg of levothyroxine sodium.Administration of the conventional formulation involves reconstitutionof the lyophilized powder in 5 milliliters (mL) of 0.9% sodium chlorideinjection (USP), to provide injectable solutions having levothyroxinesodium concentrations of 40 micrograms per milliliter (μg/mL) or 100μg/mL, respectively.

It is desirable to provide a new formulation of levothyroxine sodiumthat can further improve the stability of the levothyroxine. Preferablya new formulation of levothyroxine sodium would have acceptablestability above room temperature for an extended period of time. It isalso desirable for the new formulation to be convenient to store, toreconstitute, and to administer to a patient.

SUMMARY

A composition is provided that includes from 100 to 500 micrograms oflevothyroxine sodium, and from 1 to 5 milligrams mannitol. Thecomposition is a solid.

A composition is provided that includes from 100 to 200 micrograms oflevothyroxine sodium, and mannitol. The mass ratio of mannitol tolevothyroxine sodium is at most 40:1, and the composition is a solid.

A composition is provided that includes about 500 micrograms oflevothyroxine sodium, and mannitol. The mass ratio of mannitol tolevothyroxine sodium is at most 10:1, and the composition is a solid.

A plurality of compositions is provided, where each composition includesfrom 100 to 500 micrograms of levothyroxine sodium and from 1 to 5milligrams mannitol, and each composition is a solid. The amount oflevothyroxine sodium in each composition spans the range of 100 to 500micrograms. The amount of mannitol is substantially the same in eachcomposition. When the plurality of compositions is stored at 25° C., atmost 0.20% of the levothyroxine sodium in each composition is convertedto liothyronine over a period of 12 months.

A solid composition is provided, which is formed by a method thatincludes combining ingredients to form a liquid mixture, andlyophilizing the liquid mixture. The ingredients include a solvent,levothyroxine sodium, mannitol, and substantially no tribasic sodiumphosphate.

A solid composition is provided, which is formed by a method thatincludes combining ingredients to form a liquid mixture, andlyophilizing the liquid mixture. The ingredients include a solvent,levothyroxine sodium, mannitol and dibasic sodium phosphate. The massratio of mannitol to levothyroxine sodium in the liquid mixture is atmost 40:1.

To provide a clear and more consistent understanding of thespecification and claims of this application, the following definitionsare provided.

The term “mass ratio” of two substances means the mass of one substance(S1) relative to the mass of the other substance (S2), where both masseshave identical units, expressed as S1:S2.

The term “lyophilizing” means removing from a solution or an emulsionone or more substances having the lowest boiling points by freezing thesolution or emulsion and applying a vacuum to the frozen mixture.

The term “spans the range”, with regard to a range of the amount of asubstance in a plurality of compositions, means that at least one of thecompositions contains the substance in an amount corresponding to thelowest end of the range, at least one of the compositions contains thesubstance in an amount corresponding to the highest end of the range,and the remaining compositions, if any, contain the substance in anamount within the range. For example, in a plurality of compositions inwhich the amount of levothyroxine sodium spans the range of 100-500 μg,at least one of the compositions contains 100 μg levothyroxine sodium,at least one of the other compositions contains 500 μg levothyroxinesodium, and the remaining compositions, if any, contain from 100 μg to500 μg levothyroxine sodium.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood with reference to the followingdrawing and description. The components in the figure are notnecessarily to scale and are not intended to accurately representmolecules or their interactions, emphasis instead being placed uponillustrating the principles of the invention.

FIG. 1 depicts a chemical structure of levothyroxine sodium.

FIG. 2 depicts graphs of the amount of liothyronine (T3) impurity overtime at 40° C. for compositions containing 100 μg (“mcg”; squaresymbols), 200 μg (triangle symbols) or 500 μg (circle symbols)levothyroxine sodium (L), and either 3 mg (open symbols) or 10 mg (opensymbols) mannitol (M).

FIG. 3 depicts graphs of the amount of T3 impurity over time at 25° C.for compositions containing 100 μg (“mcg”; square symbols), 200 μg(triangle symbols) or 500 μg (circle symbols) levothyroxine sodium (L),and either 3 mg (open symbols) or 10 mg (open symbols) mannitol (M).

DETAILED DESCRIPTION

Lyophilized levothyroxine sodium compositions that include less mannitolthan conventional compositions can protect levothyroxine fromdegradation at temperatures of 25° C. and higher. These compositionsalso can maintain a consistent level of levothyroxine over a wide rangeof dosages. Reconstitution of the lyophilized compositions with acarrier liquid can yield injectable liquids having ingredients that aremore acceptable than those in conventional compositions.

A levothyroxine composition may include levothyroxine sodium, mannitol,and optionally one or more other substances, where the composition is asolid. Improved stability of levothyroxine can be achieved by loweringthe mass of mannitol and/or the mass ratio of mannitol to levothyroxinesodium in the composition to a level below that of conventionallevothyroxine compositions. Conventional levothyroxine compositionsinclude 10 milligrams (mg) mannitol and either 200 or 500 micrograms(μg) levothyroxine sodium, corresponding to mass ratios of mannitol tolevothyroxine sodium (M:L) of 50:1 and 20:1, respectively. In contrast,improved stability of levothyroxine can be obtained in compositionshaving either 200 or 500 μg levothyroxine sodium by lowering the amountof mannitol to 1 to 5 milligrams, corresponding to M:L ratios of from5:1 to 25:1 and from 2:1 to 10:1, respectively.

Solid levothyroxine compositions may be prepared by forming a liquidmixture containing a solvent, levothyroxine sodium and mannitol, andlyophilizing the liquid mixture. Forming a liquid mixture for use inpreparing the solid composition may include combining ingredientsincluding a solvent, levothyroxine sodium and mannitol. The ingredientsalso may include a phosphate buffer; however the ingredients preferablydo not include tribasic sodium phosphate.

A solid composition that includes levothyroxine sodium and mannitol mayinclude from 25 to 1,000 μg levothyroxine sodium. Preferably thecomposition includes from 50 to 750 μg levothyroxine sodium, or from 100to 500 μg levothyroxine sodium. The amount of levothyroxine sodium inthe composition may be an amount sufficient for a single initial dose oflevothyroxine sodium, an amount sufficient for a single 2^(nd) day doseof levothyroxine sodium, or an amount sufficient for a daily maintenancedose of levothyroxine sodium. The amount of levothyroxine sodium in thecomposition may be a different therapeutic amount. For example, theamount of levothyroxine sodium in the composition may be an amountsufficient for half of a single initial dose, half of a single 2^(nd)day dose, or half of a daily maintenance dose. Presently preferredamounts of levothyroxine sodium in the composition include about 100 μg,about 200 μg, and about 500 μg.

A solid composition that includes levothyroxine sodium and mannitol mayinclude one or more other substances. Non-limiting examples of othersubstances include bulking agents, carriers, diluents, fillers, salts,buffers, stabilizers, solubilizers, preservatives, antioxidants, andtonicity contributors. Substances that may be useful in formulatingpharmaceutically acceptable compositions, and methods of forming suchcompositions, are described for example in Remington: The Science andPractice of Pharmacy, 20th Ed., ed. A. Gennaro, Lippincott Williams &Wilkins, 2000, and in Kibbe, “Handbook of Pharmaceutical Excipients,”3′Edition, 2000.

A solid composition that includes levothyroxine sodium and mannitol maybe prepared by forming a liquid mixture containing a solvent,levothyroxine sodium and mannitol, and lyophilizing the liquid mixture.Forming a liquid mixture for use in preparing the solid composition mayinclude combining ingredients including the solvent, levothyroxinesodium and mannitol. The ingredients used to form the liquid mixture mayinclude a phosphate buffer; however the ingredients preferably do notinclude tribasic sodium phosphate. In one example, the ingredients usedto form the liquid mixture include a phosphate buffer other thantribasic sodium phosphate, such as dibasic sodium phosphate (Na₂HPO₄) ormonobasic sodium phosphate (NaH₂PO₄). The amount of phosphate buffer inthe ingredients may be an amount sufficient to provide a beneficial pHbuffering effect in the liquid mixture. Preferably the ingredients usedto form the liquid mixture include from 100 to 800 μg, from 200 to 700μg, from 300 to 700 μg, or from 400 to 600 μg dibasic sodium phosphate.Dibasic sodium phosphate may be added as a hydrate, such as dibasicsodium phosphate heptahydrate.

Forming the liquid mixture for use in preparing the solid compositionmay further include adding a base to the liquid mixture to provide adesired pH in the mixture, where the base is different from any bufferspresent in the composition, such as a phosphate buffer. The amount ofthe base added to the liquid mixture may be an amount sufficient toprovide a liquid mixture pH in the range of 10.5 to 12.5 or from 11 to12. The amount of the base may be an amount sufficient to provide a pHin the range of 9.5 to 11.5 or of 10 to 11 when a solid compositionformed from the liquid mixture is subsequently reconstituted in 5 mL of0.9% aqueous sodium chloride (USP). Presently preferred bases includesodium hydroxide.

A solid composition that includes levothyroxine sodium and mannitol mayinclude from 25 μg to less than 10 mg mannitol. Preferably thecomposition includes from 0.1 to 7 mg mannitol, from 1 to 5 mg mannitol,from 2 to 4 mg mannitol, or from 2.9 to 3.1 mg mannitol. The amount ofmannitol in the composition may be an amount sufficient to provide abeneficial bulking effect to the solid composition, while maintaining aM:L ratio less than 50:1, and preferably of 40:1 or less. For example, asolid composition that includes levothyroxine sodium and mannitol mayhave a M:L ratio less than 50:1, or at most 40:1. Preferably thecomposition has a M:L ratio of from 1:1 to 40:1, from 5:1 to 35:1, orfrom 6:1 to 30:1. Presently preferred M:L ratios include about 6:1,about 15:1 and about 30:1. For compositions that include less than 500μg levothyroxine sodium, the mass ratio of mannitol to levothyroxinesodium preferably is at most 40:1. For compositions that include atleast 500 μg levothyroxine sodium, the mass ratio of mannitol tolevothyroxine sodium preferably is at most 10:1.

It has been discovered that, in a solid composition that includeslevothyroxine sodium and mannitol, the stability of levothyroxine may beimproved by lowering the amount of mannitol in the composition to alevel below that of conventional compositions. Conventionallevothyroxine compositions include either 200 or 500 μg levothyroxinesodium, and include 10 mg mannitol. In contrast, levothyroxine may haveimproved stability at room temperature and at elevated temperatures whenpresent in solid compositions that include 100, 200 or 500 μglevothyroxine sodium and include less than 10 mg mannitol.

The stability of levothyroxine was analyzed for solid compositions thatcontained 100 μg levothyroxine sodium and from 2 mg to 10 mg mannitol.The solid compositions were formed by combining water, the levothyroxinesodium, the mannitol, and 500 μg dibasic sodium phosphate to form liquidmixtures, and then adding sodium hydroxide to provide a pH of about11.8. Water for injection (USP) was added to each liquid mixture asneeded to provide total volumes of 1 milliliter (mL). The liquidmixtures were lyophilized to provide solid compositions, which were thenstored in amber tinted vials at temperatures of 40° C. or 55° C. Thestability of the levothyroxine in the solid compositions at differenttemperatures was determined by measuring the amount of liothyronine (T3)in each composition over time, as T3 is a degradation product oflevothyroxine (T4). The results of these measurements are listed inTable 1, below.

TABLE 1 Stability of levothyroxine in solid compositions containingdifferent amounts of mannitol. Levothyroxine Sodium: 100 μg 100 μg 100μg 100 μg Dibasic Sodium Phosphate: 500 μg 500 μg 500 μg 500 μgMannitol: 10 mg 4 mg 3 mg 2 mg M:L ratio: 100:1 40:1 30:1 20:1 TimeTemp. % T3 0 — 0.17 0.22 0.22 0.22 1 month 40° C. 0.34 0.19 0.18 0.18 2months 0.30 0.18 0.18 0.19 3 months 0.57 0.18 0.18 0.18 2 week 55° C. —0.18 0.18 0.19 4 weeks — 0.19 0.18 0.19

The results listed in Table 1 show that levothyroxine was more stable inthe compositions containing less than 10 mg mannitol than in thecomposition containing a conventional amount of mannitol of 10 mg. Thecompositions having improved stability contained 4 mg, 3 mg or 2 mgmannitol, whereas the least stable composition contained a conventionalamount of mannitol of 10 mg. The compositions having improved stabilityalso had M:L ratios of at most 40:1, whereas the M:L ratio of thecomposition containing a conventional amount of mannitol was 100:1.

As shown in Table 1, during storage at 40° C. the amount of T3 in thecomposition containing 10 mg mannitol varied from 0.30% to 0.57% over aperiod of from 1 to 3 months, a range of approximately 90%[90.0%=100%×(0.57−0.30)/0.30]. In contrast, the amount of T3 in thecompositions containing from 2 mg to 4 mg mannitol remained relativelystable under the same conditions, varying only by approximately 6%[5.6%=100%×(0.19−0.18)/0.18)]. In the compositions containing 2 to 4 mgmannitol, at most 0.19% of the levothyroxine sodium was converted toliothyronine when stored at 40° C. over a period of 3 months.

As shown in Table 1, the compositions containing less than 10 mgmannitol maintained the stability of levothyroxine when stored at aneven higher temperature of 55° C. During storage at 55° C. over a periodof from 2 to 4 weeks, the amount of T3 in the compositions containingfrom 2 mg to 4 mg mannitol varied only by approximately 6%[5.6%=100%×(0.19−0.18)/0.18)]. In the compositions containing 2 to 4 mgmannitol, at most 0.19% of the levothyroxine sodium was converted toliothyronine when stored at 55° C. over a period of 4 weeks.

The surprising and unexpected improvement in levothyroxine stability ina solid composition upon lowering the amount of mannitol in thecomposition also was observed in solid compositions that contained morethan 100 μg levothyroxine sodium. The stability of levothyroxine wasanalyzed for solid compositions that contained from 100 μg to 500 μglevothyroxine sodium and 3 mg mannitol. The solid compositions wereformed by combining water, the levothyroxine sodium, the mannitol, and500 μg dibasic sodium phosphate to form liquid mixtures, and then addingsodium hydroxide to provide a pH of about 11.8. Water for injection(USP) was added to each liquid mixture as needed to provide totalvolumes of 1 mL. The liquid mixtures were lyophilized to provide solidcompositions, which were then stored in amber tinted vials attemperatures of 25° C. or 40° C. The stability of the levothyroxine inthe solid compositions at different temperatures was determined bymeasuring the amount of T3 in each composition over time, as describedabove. The results of these measurements are listed in Table 2, below.Each entry in this table represents an average of 3 measurements.

TABLE 2 Stability of levothyroxine in solid compositions containingdifferent amounts of levothyroxine sodium and 3 mg mannitol.Levothyroxine Sodium: 100 μg 200 μg 500 μg Dibasic Sodium Phosphate: 500μg 500 μg 500 μg Mannitol: 3 mg 3 mg 3 mg M:L ratio: 30:1 15:1 6:1 Time(mo.) Temperature % T3 0 — 0.12 0.12 0.12 1 40° C. 0.13 0.13 0.13 2 0.130.13 0.14 3 0.13 0.13 0.13 6 0.13 0.14 0.13 3 25° C. 0.13 0.13 0.13 60.12 0.12 0.12 9 0.13 0.13 0.13 12 0.12 0.12 0.12

The results listed in Table 2 show that levothyroxine was stable at roomtemperature and at an elevated temperature of 40° C. when present at avariety of amounts, in solid compositions that included only 3 mgmannitol. The compositions containing 100 μg, 200 μg or 500 μglevothyroxine sodium and having improved stability contained 3 mgmannitol, whereas conventional levothyroxine compositions that contain200 μg or 500 μg levothyroxine sodium include 10 mg mannitol. Thecomposition containing 200 μg levothyroxine sodium and having improvedstability had a M:L ratio of only 15:1, whereas the M:L ratio of aconventional composition containing 200 μg levothyroxine sodium is 50:1.The composition containing 500 μg levothyroxine sodium and havingimproved stability had a M:L ratio of only 6:1, whereas the M:L ratio ofa conventional composition containing 500 μg levothyroxine sodium is20:1.

As shown in Table 2, during storage at 25° C. the amount of T3 in thecompositions containing 3 mg mannitol varied only by approximately 8%over a period of from 3 to 12 months [8.3%=100%×(0.13−0.12)/0.12)]. Asimilar variation in the amount of T3 was observed when the samecompositions were stored at an elevated temperature of 40° C. over aperiod of from 1 to 6 months [7.7%=100%×(0.14−0.13)/0.13)].

Solid compositions that include levothyroxine sodium and mannitolpreferably can protect levothyroxine from degradation for a year orlonger at room temperature (25° C.), and for 6 months or longer atelevated temperatures. Referring to Table 2, each of the listed solidcompositions maintained the level of T3 impurity below 0.15% for oneyear at 25° C. and for 6 months at 40° C. As shown in Table 2, in all ofthe compositions listed, at most 0.13% of the levothyroxine sodium wasconverted to liothyronine when stored at 25° C. over a period of 12months. Similarly, in all of the compositions listed, at most 0.14% ofthe levothyroxine sodium was converted to liothyronine when stored at40° C. over a period of 3 months or 6 months.

Preferably, when a solid composition that includes levothyroxine sodiumand mannitol is stored at 25° C., at most 0.20% of the levothyroxinesodium is converted to liothyronine (T3) over a period of 12 months.Preferably, when a solid composition that includes levothyroxine sodiumand mannitol is stored at 25° C., at most 0.15% or at most 0.14% of thelevothyroxine sodium is converted to liothyronine over a period of 12months.

Preferably, when a solid composition that includes levothyroxine sodiumand mannitol is stored at 40° C., at most 0.20% of the levothyroxinesodium is converted to liothyronine over a period of 3 months.Preferably, when a solid composition that includes levothyroxine sodiumand mannitol is stored at 40° C., at most 0.15% of the levothyroxinesodium is converted to liothyronine over a period of 3 months or over aperiod of 6 months. Preferably, when a solid composition that includeslevothyroxine sodium and mannitol is stored at 40° C., at most 0.14% ofthe levothyroxine sodium is converted to liothyronine over a period of 3months or over a period of 6 months.

Preferably, when a solid composition that includes levothyroxine sodiumand mannitol is stored at 55° C., at most 0.20% of the levothyroxinesodium is converted to liothyronine over a period of 4 weeks.Preferably, when a solid composition that includes levothyroxine sodiumand mannitol is stored at 55° C., at most 0.19% of the levothyroxinesodium is converted to liothyronine over a period of 4 weeks.

The results listed in Table 2 also show that levothyroxine was stable atroom temperature and at an elevated temperature of 40° C. across adosage range of 100 to 500 μg levothyroxine sodium. While the amount oflevothyroxine sodium spanned the range of 100 μg to 500 μg, the amountof mannitol and phosphate buffer were substantially the same for eachcomposition. Surprisingly, there was no significant difference in theinitial T3 levels between these solid compositions, even though theamount of levothyroxine sodium in the compositions varied from 100 μg to500 μg. Moreover, there was no significant difference in the T3 levelsbetween the solid compositions over time, either at room temperature orat an elevated temperature. As shown in Table 2, in the plurality ofcompositions listed, at most 0.13% of the levothyroxine sodium in eachof the compositions was converted to liothyronine when stored at 25° C.over a period of 12 months, and at most 0.14% of the levothyroxinesodium in each of the compositions was converted to liothyronine whenstored at 40° C. over a period of 3 months or 6 months.

Solid compositions that include levothyroxine sodium and mannitolpreferably can maintain a consistent level of pure levothyroxine,regardless of the concentration of the levothyroxine sodium in thecomposition. Preferably, when a plurality of solid compositions thatinclude levothyroxine sodium and mannitol are stored at 25° C., wherethe amount of levothyroxine sodium spans the range of 100 μg to 500 μgand the amount of mannitol and any optional buffer are substantially thesame for each composition, at most 0.20% of the levothyroxine sodium ineach of the solid compositions is converted to liothyronine over aperiod of 12 months. Preferably, when a plurality of solid compositionsthat include levothyroxine sodium and mannitol are stored at 25° C.,where the amount of levothyroxine sodium spans the range of 100 μg to500 μg and the amount of mannitol and any optional buffer aresubstantially the same for each composition, at most 0.15% or at most0.14% of the levothyroxine sodium in each of the solid compositions isconverted to liothyronine over a period of 12 months. Preferably, when aplurality of solid compositions that include levothyroxine sodium andmannitol are stored at 40° C., where the amount of levothyroxine sodiumspans the range of 100 μg to 500 μg and the amount of mannitol and anyoptional buffer are substantially the same for each composition, at most0.15% or at most 0.14% of the levothyroxine sodium in each of the solidcompositions is converted to liothyronine over a period of 3 months orover a period of 6 months.

FIG. 2 depicts graphs of liothyronine (T3) impurity over time at 40° C.for compositions containing 100 μg (“mcg”), 200 μg or 500 μglevothyroxine sodium (L), and either 3 mg or 10 mg mannitol (M). FIG. 3depicts graphs of T3 impurity over time at 25° C. for compositionscontaining 100 μg, 200 μg or 500 μg levothyroxine sodium, and either 3mg or 10 mg mannitol. The graphs in FIGS. 2 and 3 for the compositionscontaining 3 mg mannitol (open symbols) correspond to the results listedin Table 2. The graphs in FIGS. 2 and 3 for the compositions containing10 mg mannitol (closed symbols) correspond to results of an analysis ofthe stability of levothyroxine in solid compositions containing 100 μg,200 μg or 500 μg levothyroxine sodium and 10 mg mannitol. These solidcompositions were formed by combining water, the levothyroxine sodium,the mannitol, and 500 μg dibasic sodium phosphate to form liquidmixtures, and then adding sodium hydroxide to provide a pH of about11.8. Water for injection (USP) was added to each liquid mixture asneeded to provide total volumes of 1 mL. The liquid mixtures werelyophilized to provide solid compositions, which were then stored invials at temperatures of 25° C. or 40° C. The stability of thelevothyroxine in the solid compositions over time at differenttemperatures was determined by measuring the amount of T3, as describedabove. The results of these measurements for the compositions containing10 mg mannitol are listed in Table 3, below.

TABLE 3 Stability of levothyroxine in solid compositions containingdifferent amounts of levothyroxine sodium and 10 mg mannitol.Levothyroxine Sodium: 100 μg 200 μg 500 μg Dibasic Sodium Phosphate: 500μg 500 μg 500 μg Mannitol: 10 mg 10 mg 10 mg M:L ratio: 100:1 50:1 20:1Time (mo.) Temp (° C.) % T3 0 — 0.17 0.18 0.17 1 40 0.34 0.21 0.20 20.30 0.23 0.21 3 0.57 0.32 0.20 2 25 0.20 0.19 0.17 3 0.22 0.19 0.17 60.25 0.21 0.20 9 0.24 0.24 0.19 12 0.29 0.21 0.19 18 0.35 0.24 0.21

The results depicted in FIG. 2 show that the solid compositionscontaining only 3 mg mannitol maintained lower T3 levels at 40° C. overtime than did the corresponding compositions containing mannitol at aconventional level of 10 mg. The instability of levothyroxine incompositions containing 10 mg mannitol over time, as indicated by higherT3 levels, was inversely related to the amount of levothyroxine sodiumin the compositions. Solid compositions containing 100 μg levothyroxinesodium and 10 mg mannitol (M:L ratio of 100:1) had higher T3 levels overtime than did solid compositions containing 200 μg levothyroxine sodiumand 10 mg mannitol (M:L ratio of 50:1), which in turn had higher T3levels over time than did solid compositions containing 500 μglevothyroxine sodium and 10 mg mannitol (M:L ratio of 20:1).

The results depicted in FIG. 3 show that the solid compositionscontaining only 3 mg mannitol also maintained lower T3 levels at 25° C.over time than did the corresponding compositions containing mannitol ata conventional level of 10 mg. The instability of levothyroxine incompositions containing 10 mg mannitol over time was not as pronouncedat 25° C. as it was at 40° C. The inverse relationship betweenlevothyroxine instability and the amount of levothyroxine sodium inthese compositions, as described above, was observed from month 2 tomonth 6.

The results of Tables 1 and 2 and FIGS. 2 and 3 show that the stabilityof levothyroxine in a solid composition may be improved by lowering theamount of mannitol and/or the mass ratio of mannitol to levothyroxinesodium (M:L) in the composition to a level below that of conventionalcompositions. Solid compositions containing 100-500 μg levothyroxinesodium and less than 10 mg mannitol may be more stable than solidcompositions containing 100-500 μg levothyroxine sodium and aconventional amount of 10 mg mannitol. Solid compositions containing100-200 μg levothyroxine sodium and having a M:L ratio of 40:1 or lowermay be more stable than solid compositions containing 100-200 μglevothyroxine sodium and having a conventional M:L ratio of 50:1 orgreater. Solid compositions containing 500 μg levothyroxine sodium andhaving a M:L ratio of 10:1 or lower may be more stable than solidcompositions containing 500 μg levothyroxine sodium and having aconventional M:L ratio of 20:1.

A solid composition that includes levothyroxine sodium and mannitol maybe prepared by forming a liquid mixture containing a solvent,levothyroxine sodium, mannitol and optionally one or more othersubstances, and lyophilizing the mixture. The lyophilizing may includefreeze-drying the liquid mixture to provide a solid composition. Theliquid mixture may be prepared by combining ingredients includinglevothyroxine sodium and mannitol in the amounts described above. Theliquid mixture may further include a phosphate buffer, a base and/or oneor more other substances, as described above.

The liquid mixture may include from 0.1 to 5 mL solvent, from 25 to1,000 μg levothyroxine sodium, and from 25 μg to 10 mg mannitol. Theliquid mixture may include from 0.5 to 2 mL solvent, from 50 to 750 μglevothyroxine sodium, and from 0.1 to 5 mg mannitol. The liquid mixturemay include from 0.75 to 1.5 mL solvent, from 50 to 750 μg levothyroxinesodium, and from 1 to 3 mg mannitol. The mass ratio of mannitol tolevothyroxine sodium (M:L) in the liquid mixture may be from 1:1 to40:1, from 5:1 to 35:1, or from 6:1 to 30:1.

The ingredients combined to form a liquid mixture containing a phosphatebuffer may include from 0.1 to 5 mL solvent, from 25 to 1,000 μglevothyroxine sodium, from 25 μg to less than 10 mg mannitol, and from100 to 800 μg dibasic sodium phosphate. The ingredients may include from0.5 to 2 mL solvent, from 50 to 750 μg levothyroxine sodium, from 0.1 to7 mg mannitol, and from 200 to 700 μg dibasic sodium phosphate. Theingredients may include from 0.75 to 1.5 mL solvent, from 100 to 500 μglevothyroxine sodium, from 1 to 5 mg mannitol, and from 400 to 600 μgdibasic sodium phosphate. The mass ratio of mannitol to levothyroxinesodium in the liquid mixture may be from 1:1 to 40:1, from 5:1 to 35:1,or from 6:1 to 30:1. Preferably the ingredients are substantially freeof tribasic sodium phosphate.

The solvent, levothyroxine sodium, mannitol, optional buffer, optionalbase and one or more other optional substances may be combined in anyorder when forming the liquid mixture. For example, a liquid mixture maybe formed by adding the levothyroxine sodium and mannitol to a containerincluding the solvent, and then adding a buffer and/or a base to achievethe desired pH in the liquid mixture. The liquid mixture preferably hasa pH of from 11 to 12. A presently preferred pH of the liquid mixture is11.8±0.1.

The solvent in the liquid mixture may include water and/or an organicsolvent. If the solvent includes an organic solvent, the organic solventpreferably is miscible with water. Non-limiting examples of organicsolvents that are miscible with water and may be present in the solventinclude alcohols such as ethanol, isopropanol, and t-butanol. Theconcentration of organic solvent, if present, may be from 1 to 20percent by volume (vol %) or from 2 to 10 vol % of the solvent. Theliquid mixture may include from 0.1 to 5 mL solvent. Preferably theliquid mixture includes from 0.5 to 2 mL solvent, or from 0.75 to 1.5 mLsolvent.

The liquid mixture including the solvent, levothyroxine sodium,mannitol, and any other optional ingredients may be lyophilized to forma solid composition, such as by subjecting the liquid mixture tofreeze-drying. Freeze-drying of the liquid mixture may includemaintaining the liquid mixture in an inert atmosphere, such as nitrogenor argon. Preferably the liquid mixture is placed in glass vials priorto lyophilization, and the amount of the liquid mixture in each vial isbased on the amount of levothyroxine intended to be present in the finalsolid composition in the vial.

In a typical lyophilization process, the temperature of the liquidmixture is lowered to a temperature at or below the solidification pointof the liquid mixture. If the liquid mixture forms a glass when cooled,the solidification point typically is the glass transition temperature.If the liquid mixture forms crystals when cooled, the solidificationpoint typically is the eutectic point. The solidified mixture is thendried under vacuum. Typically, the drying process includes a primarydrying step in which the temperature of the solidified mixture is raisedgradually while most of the water is removed from the mixture by thevacuum, and a secondary drying step in which the temperature of thesolidified mixture is raised further while residual moisture is removedfrom the mixture by the vacuum. The temperature is kept at or below thedesired storage temperature for the final solid composition.Lyophilization typically is complete within 48 hours, but may requireadditional time. The solid composition resulting from the lyophilizationtypically is sealed for later use. Details regarding the lyophilizationprocess may be found, for example, in Remington: The Science andPractice of Pharmacy, 20th Ed., ed. A. Gennaro, Lippincott Williams &Wilkins, 2000.

The lyophilized solid composition may be stored for later reconstitutionand administration. Preferably the solid composition is stored at atemperature of 10° C. to 40° C., from 15° C. to 35° C., from 20° C. to30° C., or about 25° C. Preferably the solid composition is protectedfrom light, such as by storing the composition in an opaque or tintedcontainer, such as an amber tinted container. Preferably the solidcomposition is sealed in a glass vial to protect the composition frommoisture in the surrounding environment. Presently preferred containersinclude amber tinted glass vials.

A solid composition that includes levothyroxine sodium and mannitol maybe administered to a patient by combining the composition with anaqueous carrier liquid to form an aqueous mixture, and administering theaqueous mixture into the patient by, for example, injection. Preferably,the aqueous carrier liquid is a pharmaceutically acceptable carrierliquid. Non-limiting examples of pharmaceutically acceptable carrierliquids include water and saline, such as phosphate buffered saline(PBS), Ringers solution or lactated Ringers injection. The aqueouscarrier liquid also may include fixed oils, fatty esters or polyols,particularly if the aqueous mixture for injection is a suspension. Theaqueous carrier liquid also may include one or more other substancessuch as buffers, stabilizers, solubilizers, preservatives andantioxidants. Preferably the solid composition dissolves in the aqueouscarrier liquid to form a solution. Presently preferred aqueous carrierliquids include sodium chloride injection, such as solutions containing0.9%, 0.45% or 0.225% sodium chloride. Presently preferred aqueouscarrier liquids include 0.9% sodium chloride injection, 0.9% sodiumchloride injection USP containing benzyl alcohol, and bacteriostaticsodium chloride injection.

The amount of aqueous carrier liquid may be sufficient to provide anaqueous mixture containing levothyroxine sodium at a concentration offrom 5 to 500 μg/mL. Preferably the concentration of levothyroxinesodium in the aqueous mixture is from 10 to 200 μg/mL, or from 20 to 100μg/mL. Presently preferred concentrations of levothyroxine sodium in anaqueous mixture for injection include about 20 μg/mL, 40 μg/mL and 100μg/mL.

An aqueous mixture formed from the solid composition may be administeredto provide an initial dose of 200-500 μg or of 300-500 μg oflevothyroxine sodium to a patient. An aqueous mixture formed from thesolid composition may be administered to provide a 2^(nd) day dose of100-300 μg of levothyroxine sodium to a patient. An aqueous mixtureformed from the solid composition may be administered to provide a dailydose of 50-100 μg of levothyroxine sodium to a patient. Doses outside ofthese ranges also may be administered.

While various embodiments of the invention have been described, it willbe apparent to those of ordinary skill in the art that other embodimentsand implementations are possible within the scope of the invention.Accordingly, the invention is not to be restricted except in light ofthe attached claims and their equivalents.

What is claimed is:
 1. A composition, comprising: about 100 or about 200micrograms of levothyroxine sodium; a phosphate buffer; and from 2 to 4milligrams of mannitol, where the composition is a lyophilized solid. 2.The composition of claim 1, where the amount of levothyroxine sodium isabout 100 micrograms and the amount of mannitol is about 3 milligrams.3. The composition of claim 1, where the amount of levothyroxine sodiumis about 200 micrograms and the amount of mannitol is about 3milligrams.
 4. The composition of claim 2, where the phosphate buffer isdibasic sodium phosphate in an amount from 400 to 600 micrograms.
 5. Thecomposition of claim 4, where the composition is formed by forming aliquid mixture by combining the levothyroxine sodium, the mannitol,dibasic sodium phosphate, and a solvent comprising water; andlyophilizing the liquid mixture.
 6. The composition of claim 1, wherewhen the composition is stored at 25 ° C., at most 0.20% of thelevothyroxine sodium is converted to liothyronine over a period of 12months.
 7. The composition of claim 1, where when the composition isstored at 40 ° C., at most 0.20% of the levothyroxine sodium isconverted to liothyronine over a period of 3 months.
 8. The compositionof claim 4, where when the composition is stored at 25 ° C., at most0.20% of the levothyroxine sodium is converted to liothyronine over aperiod of 12 months.
 9. The composition of claim 3, where the phosphatebuffer is dibasic sodium phosphate in an amount from 400 to 600micrograms.
 10. The composition of claim 9, where the composition isformed by forming a liquid mixture by combining the levothyroxinesodium, the mannitol, dibasic sodium phosphate, and a solvent comprisingwater; and lyophilizing the liquid mixture.
 11. The composition of claim4, where when the composition is stored at 40 ° C., at most 0.20% of thelevothyroxine sodium is converted to liothyronine over a period of 3months.
 12. The composition of claim 9, where when the composition isstored at 25 ° C., at most 0.20% of the levothyroxine sodium isconverted to liothyronine over a period of 12 months.
 13. Thecomposition of claim 9, where when the composition is stored at 40 ° C.,at most 0.20% of the levothyroxine sodium is converted to liothyronineover a period of 3 months.
 14. A composition, comprising: about 500micrograms of levothyroxine sodium; a phosphate buffer; and from 2 to 4milligrams of mannitol, where the composition is a lyophilized solid.15. The composition of claim 14, where the amount of mannitol is about 3milligrams.
 16. The composition of claim 15, where the phosphate bufferis dibasic sodium phosphate in an amount from 400 to 600 micrograms. 17.The composition of claim 16, where the composition is formed by forminga liquid mixture by combining the levothyroxine sodium, the mannitol,dibasic sodium phosphate, and a solvent comprising water; andlyophilizing the liquid mixture.
 18. The composition of claim 14, wherewhen the composition is stored at 25 ° C., at most 0.15% of thelevothyroxine sodium is converted to liothyronine over a period of 12months.
 19. The composition of claim 16, where when the composition isstored at 25 ° C., at most 0.15% of the levothyroxine sodium isconverted to liothyronine over a period of 12 months.
 20. Thecomposition of claim 16, where when the composition is stored at 40 °C., at most 0.15% of the levothyroxine sodium is converted toliothyronine over a period of 3 months.
 21. The composition of claim 14,where when the composition is stored at 40 ° C., at most 0.15% of thelevothyroxine sodium is converted to liothyronine over a period of 3months.